Screening of “Cry for Help” Signals from Angelica sinensis Induced by Fusarium solani and Their Potential for Biological Control

Background: Root rot caused by Fusarium solani is a devastating disease in Angelica sinensis (danggui), leading to severe yield and quality losses. Sustainable control strategies are urgently needed. According to the plant “cry for help” theory, plants under pathogen attack may recruit beneficial microbes via root exudates. However, whether A. sinensis employs this strategy against F. solani remains unknown. This study aimed to identify potential “cry for help” metabolites and evaluate their biocontrol potential. Methods: LC-MS analysis revealed that F. solani infection significantly altered the metabolic profiles of both A. sinensis roots and rhizosphere soil. Results: Comparative analysis identified seven metabolites specifically upregulated in infected plants but not detected in the pathogen, including taurine, oxoadipic acid, quinolinic acid, 6-phosphogluconic acid, methyl cinnamate, 2-phenylethanol, and (R)-3-hydroxybutyric acid. Exogenous application of these seven metabolites revealed that taurine and methyl cinnamate significantly alleviated disease symptoms, improved plant growth (root length, biomass), and enhanced the activities of key defense enzymes (peroxidase, POD, phenylalanine ammonia-lyase, PAL, lipoxygenase, LOX, polyphenol oxidase, PPO). Furthermore, taurine and methyl cinnamate reshaped the rhizosphere microbiome. The incidence of root rot was reduced by 51.3% and 50.8%, respectively. Taurine enriched actinobacteria (e.g., Paeniglutamicibacter) and reduced the relative abundance of pathogenic Ascomycota fungi, while methyl cinnamate markedly enriched the nitrogen-fixing bacterium Azotobacter and the saprophytic fungus Schizothecium. Crucially, both treatments significantly suppressed the proliferation of F. solani in the rhizosphere. Conclusions: Our findings demonstrate for the first time that A. sinensis activates a “cry for help” response upon attack by F. solani, with taurine and methyl cinnamate preliminarily identified as key signaling metabolites that can directly or indirectly inhibit the development of A. sinensis root rot. These compounds enhance plant resistance and recruit beneficial microorganisms, offering a novel and promising ecological strategy for the green control of A. sinensis root rot.